Skip to main content

Full text of "Treatise On Applied Analytical Chemistry(Vol-1)"

See other formats


8i

few drops of dilute sulphuric acid and shaken with chloroform ; the latter
is coloured violet in presence of iodides.

5.  Chlorides.—0-5 gram is dissolved in 30 c.c. of water and 5 c.c. of
this solution, acidified with nitric acid, treated with silver nitrate until
precipitation is complete ; the precipitate is washed several times by decan-
tation and then digested with 4 c.c. of ammonium carbonate solution (i : 6)
and filtered :  the filtrate, acidified with nitric acid, should give at most a
faint milkiness.

6.  Quantitative Determination.—10 c.c   of a solution of 3 grams
of the bromide, dried at 100°, in 100 c.c. of water, are titrated with N/io-
silver nitrate in presence of potassium chromate.   The red colour should
be obtained with 25-2 c.c. of the silver solution, if the bromide is pure.
If chlorides are present, a larger quantity is required.

The volume permitted by the Italian Pharmacopoeia is 25-4 c.c. of the N/io-
silver solution.

POTASSIUM   CARBONATE

K2C03 = 138-2 (138)

Crude •potassium carbonate (crude potash] forms reddish or bluish grey,
spongy masses, deliquescent in moist air. Its impurities are more particu-
larly water, chlorides, sulphates, sulphites, sulphides, phosphates, cyanogen
compounds, potassium hydroxide, sodium carbonate and insoluble matter.
Its analysis includes determinations of the insoluble .matter, carbonate,
hydroxide, chloride, sulphate and sulphide (sulphite), which are carried
out as in sodium carbonate (q.v.), and also of the water, phosphates and
sodium salts (see below).1

Commercial pure potassium carbonate (refined potash] occurs in powder,
or in hygroscopic, white crystalline crusts extremely soluble in water.
According to the degree of refining, it may contain more or less marked
proportions of chloride, sulphate, phosphate, silicate, insoluble substances
and moisture, which are investigated as described under " Caustic Potash,"
and are. determined as in crude potash.

The chemically pure carbonate (puriss.] should contain only traces of
chloride and sulphate and is tested like potassium hydroxide (q.v.).

1.  Water.—10 grams are heated to redness in a platinum crucible, the
loss representing water.

2.  Phosphates.—5 grams are dissolved in nitric acid and filtered, the
filtrate being heated and precipitated with ammonium molybdate;   the
precipitate is dissolved in ammonia, precipitated with magnesia mixture
(see Fertilisers) and the magnesium ammonium phosphate filtered, ignited
and weighed as magnesium pyrophosphate in the ordinary way.    Mg2P207
X 1-907 = KSP04.

3.  Sodium Salts.—10 c.c. of the 10% solution of the carbonate (=i
gram of substance) are exactly neutralised with N-hydrochloric acid (to
methyl orange), heated to expel carbon dioxide (and any sulphur dioxide

1 For the Rapid Analysis of Potassium Carbonate, see also E. Baroni in L'Industria
chimica, 1904, VI, p. 164.
A.C. it should be